import 'dart:math';
import 'package:flutter/material.dart';

class SliverPersistentHeaderDemo extends StatelessWidget {
  final String ?text;

  SliverPersistentHeaderDemo({this.text}) : super();
  final data = <Color>[
    Colors.purple[50]!,
    Colors.purple[100]!,
    Colors.purple[200]!,
    Colors.purple[300]!,
    Colors.purple[400]!,
    Colors.purple[500]!,
    Colors.purple[600]!,
    Colors.purple[700]!,
    Colors.purple[800]!,
    Colors.purple[900]!,
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        // height: 500,
        child: CustomScrollView(
          slivers: <Widget>[
            _buildSliverAppBar(),
            _buildPersistentHeader('袅缈岁月，青丝银发', Color(0xffe7fcc9)),
            _buildCommonWidget(),
            _buildPersistentHeader('以梦为马，不负韶华', Color(0xffcca4ff)),
            _buildSliverList()
          ],
        ),
      ),
    );
  }

  Widget _buildCommonWidget() => SliverToBoxAdapter(
        child: Container(
          padding: EdgeInsets.symmetric(horizontal: 10),
          color: Colors.grey.withAlpha(22),
          child: ListTile(
            leading: Image.asset("assets/images/ic_test_1.png"),
            title: Text("以梦为马"),
            subtitle: Text("海子"),
            selected: true,
            contentPadding: EdgeInsets.all(5),
            trailing: Icon(Icons.more_vert),
          ),
        ),
      );

  Widget _buildPersistentHeader(String text, Color color) =>
      SliverPersistentHeader(
          pinned: true,
          delegate: _SliverDelegate(
            minHeight: 40.0,
            maxHeight: 100.0,
            child: Container(
                color: color,
                child: Center(
                  child: Text(
                    text,
                    style: TextStyle(fontSize: 18, shadows: [
                      Shadow(color: Colors.white, offset: Offset(1, 1))
                    ]),
                  ),
                )),
          ));

  Widget _buildSliverList() => SliverList(
        delegate: SliverChildBuilderDelegate(
            (_, int index) => Container(
                  alignment: Alignment.center,
                  width: 100,
                  height: 60,
                  color: data[index],
                  child: Text(
                    colorString(data[index]),
                    style: TextStyle(color: Colors.white, shadows: [
                      Shadow(
                          color: Colors.black,
                          offset: Offset(.5, .5),
                          blurRadius: 2)
                    ]),
                  ),
                ),
            childCount: data.length),
      );

  Widget _buildSliverAppBar() {
    return SliverAppBar(
      expandedHeight: 190.0,
      leading: _buildLeading(),
      title: Text('张风捷特烈'),
      actions: _buildActions(),
      elevation: 2,
      pinned: true,
      backgroundColor: Colors.orange,
      flexibleSpace: FlexibleSpaceBar(
        //伸展处布局
        titlePadding: EdgeInsets.only(left: 55, bottom: 15), //标题边距
        collapseMode: CollapseMode.parallax, //视差效果
        background: Image.asset(
          "assets/images/women_one.jpg",
          fit: BoxFit.cover,
        ),
      ),
    );
  }

  Widget _buildLeading() => Container(
      margin: EdgeInsets.all(10),
      width: 200,
      height: 50,
      child: Image.asset('assets/images/women_two.jpg'));

  List<Widget> _buildActions() => <Widget>[
        IconButton(
          onPressed: () {},
          icon: Icon(
            Icons.star_border,
            color: Colors.white,
          ),
        )
      ];

  String colorString(Color color) =>
      "#${color.value.toRadixString(16).padLeft(8, '0').toUpperCase()}";
}

class _SliverDelegate extends SliverPersistentHeaderDelegate {
  _SliverDelegate({
    @required this.minHeight,
    @required this.maxHeight,
    @required this.child,
  });

  final double ?minHeight; //最小高度
  final double ?maxHeight; //最大高度
  final Widget ?child; //孩子

  @override
  double get minExtent => minHeight!;

  @override
  double get maxExtent => max(maxHeight!, minHeight!);

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return new SizedBox.expand(child: child);
  }

  @override //是否需要重建
  bool shouldRebuild(_SliverDelegate oldDelegate) {
    return maxHeight != oldDelegate.maxHeight ||
        minHeight != oldDelegate.minHeight ||
        child != oldDelegate.child;
  }
}
